The present invention relates to a method of producing metal flakes. The invention is particularly useful for producing flakes of silver (which term as used herein, includes its alloys) having high purity, and is therefore described below with respect to this application.
Silver flakes are used in a wide variety of applications, particularly in the electronics industry for producing conductive adhesives, conductive polymers, thick films, shielding materials, printing inks, and the like. Silver flakes are generally produced by mechanically milling silver powders obtained according to various techniques, such as chemical precipitation, electrolyitc deposition, melt atomising, and salt or oxide decomposition. However, silver particles produced according to these techniques are practically of a non-porous structure, and therefore require a considerable amount of energy for deforming them into the flat flakes. Such a flattening operation is usually performed by mechanical milling which may take up to about 40 hours.
Moreover, such mechanical milling generally requires an organic lubricant, surfactant, or other organic material in order to prevent co-welding between the particles. As a result, a large amount of residual organic material remains on the flake surfaces. Such a residual material is extremely difficult, if possible at all, to completely remove because it is chemically absorbed on the silver surface. This residual organic material decreases the electrical conductivity of the silver flakes, and therefore degrades them for many uses in the electronic field where high electrical conductivity is needed.